Goal: This application seeks funds to replace an existing flow cytometry with a state-of-the-art analyzer/laser system, the MoFlo cytometer from Cytomation, Inc. Problem: The core of our present system is an Ortho Diagnostics Co. Cytofluorograph 50H flow cytometer. Our device was manufactured in February 1979 and obtained in 1980. While the instrument has provided many years of service (documentation within), it is outmoded and needs replacement for a number of related reasons: 1) service and parts are no longer available for this instrument; 2) the need by the user group for the significantly improved capabilities of newer cytometers (specifically, resolution and analysis of small organisms, yeast and bacteria, and Ca++ flux studies). Significance: This instrumentation will serve an established and productive group of investigators performing NIH-sponsored research. Current use includes DNA cell cycle analysis, cell surface immunophenotyping, and functional analysis of intracellular oxidant responses to phagocytic particle uptake. For many current users, flow cytometry is an indispensable analytical tool without which their research plan could not be executed. The instrumentation is part of a dedicated flow cytometry core facility whose personnel, service and maintenance costs are supported by an NIEHS center grant. There is an established track record of productive and cooperative use of the facility, and demonstrable needs for the expanded capabilities a new and more reliable instrument will offer. Institutional support is demonstrated by the past support of the facility, cost sharing for this instrument request, and letters of committment for future support.